Known hydraulically-actuated fuel injection systems and/or components are shown, for example, in U.S. Pat. No. 5,121,730 issued to Ausman et al. on Jun. 16, 1992; U.S. Pat. No. 5,271,371 issued to Meints et al. on Dec. 21, 1993; and U.S. Pat. No. 5,297,523 issued to Hafner et al. on Mar. 29, 1994. In these hydraulically actuated fuel injectors, a spring biased needle check opens to commence fuel injection when pressure is raised by an intensifier piston/plunger assembly to a valve opening pressure. The intensifier piston is acted upon by a relatively high pressure actuation fluid, such as engine lubricating oil, when an actuator driven actuation fluid control valve, for example a solenoid driven or piezo stack driven actuation fluid control valve, opens the injector's high pressure inlet. Injection is ended by operating the actuator to release pressure above the intensifier piston. This in turn causes a drop in fuel pressure causing the needle check to close under the action of its return spring and end injection. While these hydraulically actuated fuel injectors have performed magnificently over many years, there remains room for improvement, especially in the area of shaping an injection rate trace from beginning to end to precisely suit a set of engine operating conditions.
Over the years, engineers have discovered that engine emissions can be significantly reduced at certain operating conditions by providing a particular injection rate trace. In many cases emissions are improved when the initial injection rate is controllable, and when there is a nearly vertical abrupt end to injection. While these prior hydraulically actuated fuel injection systems have some ability to control the injection rate shape, there remains room to improve the ability to control injection rate shape with hydraulically actuated fuel injection systems.
The invention is intended to improve the ability of hydraulically actuated fuel injectors to reliably produce better injection rate shapes during each injection event.